Ion implantation is a process of introducing dopants or impurities into a substrate via bombardment. In semiconductor manufacturing, the dopants are introduced to alter electrical, optical, or mechanical properties. For example, dopants may be introduced into an intrinsic semiconductor substrate to alter the type and level of conductivity of the substrate. In manufacturing an integrated circuit (IC), a precise doping profile provides improved IC performance. To achieve an intended doping profile, one or more dopants may be implanted in the form of ions in various doses and various energy levels.
A conventional ion implantation system may comprise an ion source and a series of beam-line components. The ion source may comprise a chamber where intended ions are generated. The ion source may also comprise a power source and an extraction electrode assembly disposed near the chamber. The beam-line components, may include, for example, a mass analyzer, a first acceleration or deceleration stage, a collimator, and a second acceleration or deceleration stage. Much like a series of optical lenses for manipulating a light beam, the beam-line components can filter, focus, and manipulate ions or ion beam having intended species, shape, energy, and other qualities. The ion beam passes through the beam-line components and may be directed toward a substrate mounted on a platen or clamp. The substrate may be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a roplat.
In some applications, for example, increasing beam current to increase throughput of substrates to be implanted may be useful. Beamline ion implanters may be employed to implant substrates over a range of energies, for example, between 1 keV and 300 keV. This provides flexibility for processing substrates such as silicon wafers scheduled for various implants at differing ion energies. In order to define an implant energy, an ion beam may be subject to acceleration and/or deceleration by various components (e.g., an accelerator) in a beamline ion implanter between an ion source and substrate to be implanted.
Existing accelerators may be limited to a terminal electrode, focus electrode and ground electrode, wherein the accelerator receives the ion beam from the terminal. Except with existing accelerators, when the beam current is too high, for example, above 9 mA for a 195 keV As beam, the beam may be under-focused and thus unable to be transported through the beam-line due to beam transmission loss. Therefore, the beam current available for implanting the wafer is limited, resulting poor production throughput. On the other hand, when the beam current is too low, for example below 0.5 mA for 300 keV B+ beam, the beam may become over-focused and thus unable to be transported to the wafer properly.